In the field of material processing, it is desirable to be able from a stand-off distance to detect surface heights or densities using a laser probe. In the more specific case of chemical, biological, medical, and diagnostic applications, it is desirable to detect the presence of specific molecular structures in a sample. Many molecular structures such as cells, viruses, bacteria, toxins, peptides, DNA fragments, and antibodies are recognized by particular receptors. Biochemical technologies including gene chips, immunological chips, and DNA arrays for detecting gene expression patterns in cancer cells, exploit the interaction between these molecular structures and the receptors. [For examples see the descriptions in the following articles: Sanders, G. H. W. and A. Manz, Chip-based microsystems for genomic and proteomic analysis. Trends in Anal. Chem., 2000, Vol. 19(6), p. 364-378. Wang, J., From DNA biosensors to gene chips. Nucl. Acids Res., 2000, Vol. 28(16), p. 3011-3016; Hagman, M., Doing immunology on a chip. Science, 2000, Vol. 290, p. 82-83; Marx, J., DNA Arrays reveal cancer in its manyforms. Science, 2000, Vol. 289, p. 1670-1672]. These technologies generally employ a stationary chip prepared to include the desired receptors (those which interact with the target analyte or molecular structure under test). Since the receptor areas can be quite small, chips may be produced which test for a plurality of analytes. Ideally, many thousand binding receptors are provided to provide a complete assay. When the receptors are exposed to a biological sample, only a few may bind a specific protein or pathogen. Ideally, these receptor sites are identified in as short a time as possible.
As a separate example, both biological chips and electronic chips (including, but not limited to, semiconductor wafers) contain complex surface structures that are fabricated as part of the function of the chip. These surface features are becoming steadily smaller, scaling now into the nanometer range. Conventional laser profilometers are not able to detect such small changes. Interferometric techniques have been successfull in this range, but require stringent vibration isolation and mechanical stability to operate.
There is a need for improved interferometric and/or techniques that may be used to measure these surface structures.